Miniature slip ring and process of making the same



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March 26,1957

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u r J m 7 wwwww mhna lfi hfly 7//////// /////////////////////1 INVENTOR OLTAN N. Mzazrrr g A ORNEY March 26, 1957 z. N. MERETEY 2,786,935

MINIATURE SLIP RING AND PROCESS OF MAKING THE SAME Filed July 11, 1952 3 Sheets-Sheet 2 Fl c. 5. Fl 6. 7. Fl 0.8. Fl 6. 9.

INVENTOR I ZOLTAN N. MERETEY go f ATTORNEY March 26, 1957 MERETEY 2,786,985

MINIATURE SLIP RING AND PROCESS OF MAKING THE SAME Filed July 11, 19 52 s Shets-Sheet a FIG. l0. a Plan. Flalz. FIG. I4.

INVENTOR ZOLTAN N. MERETEY BY 14 M ATTORNEY United States Patent MINIATURE SLIP RING AND PROCESS OF MAKING THE SAME Zoltan N. Meretey, Stamford, Conn., assignor, by mesne assignments, to Breeze Corporations, Inc., Union, N. J., a corporation of New Jersey Application July 11, 1952, Serial No. 298,240

Claims. (Cl. 339-5) This invention relates to electrical conductors and a process for manufacturing the same. Electrical conductors of this type are sometimes known as slip ring or split rings.

Heretofore it has been the practice to form the insulator or main body of the assembly and then to fasten thereon the rings and connect them by means of the necessary wiring so as to produce the final assembly. This is a satisfactory method for producing massive slip ring assemblies, such as are used for automatic gun mounts and control mechanisms, radar, etc., but modern electronics have created a demand for miniature and subminiature slip ring assemblies and it is difiicult and wasteful to manufacture these assemblies by the old method.

It is an object of this invention to produce a slip ring assembly in miniature form.

It is a further object of this invention to produce a slip ring assembly having a plurality of rings mounted in a plastic insulator wherein the plastic insulator may act as a shaft for rotating parts of the assembly.

It is a still further object of this invention to produce slip ring assemblies wherein the iings are substantially less than 1 inch in diameter and have a thickness in the order of A of an inch or less. Such rings find extensive use, not only in miniature radar practice but also in the production of motors and other rotating electrical parts, where it is desired to have an electrical connection between a stationary element and a rotating element.

Heretofore in the production of miniature rings of this type it has been found necessary to form the wires about a central core and then to cast a plastic about this core and machine in the plastic a series of grooves equal in 7 number to the number of wires to be contacted and spaced apart by plastic webs that act as insulators. These grooves are cut to a depth in excess of the depth of the final ring. A hole is drilled from the bottom of this groove to contact a single wire. Frequently this drilling operation requires the use of a drill .006 inch in diameter with which drill it is necessary to go through the plastic in the bottom of the groove to contact one and only one wire of the core. This plastic is then electro-plated. so that a metal ring is formed, which is joined to the copper wire by a plug built up during this electro-plating step. This plug is of the same material as the ring.

It has been found that a superior product can be made by the following process, which process is vastly simplilied over the processes now in use, and does not lead to the high number of imperfectly produced parts. This process and the product produced thereby will be clear from the following description when read in conjunction with the drawings, in which:

Fig. l is a plan view of the comb assembly.

Fig. 2 is a sectional view of the comb and the plastic covering.

Fig. 3 is a sectional view at right angles to Fig. 2.

Fig. 4 is a sectional .view of the comb, the plastic covering, withthe ring'receiving recesses machined the-rein.

Fig. 5 is a plan view of the plastic assembly shown in Fig. 4.

Fig. 6 is a plan view of an enlargement of Fig. 5, showing the end of the conductor.

Fig. 7 is a plan view of the assembly showing the conductive coating applied thereto.

Fig. 8 is a plan view in partial section showing the plating applied thereon.

Fig. 9 is a plan view in partial section showing the finished product.

Fig. 10 is a core assembly of a second embodiment of the invention.

Fig. 11 is the core assembly shown in Fig. 10 with the plastic insulator thereon.

Fig. 12 is a core assembly with the plastic insulator cast thereon of another embodiment of the invention.

Fig. 13 is a sectional view on line 13--13 of Fig. 12.

Fig. 14 illustrates a method of molding the insulator about the core assembly.

Referring to the drawings in which like parts have similar legends: The method of manufacturing either the split or slip ring assembly is shown in Figure 1 wherein the first step comprises the formation of a seriesof insulated conductors 21, 22, 23, 24, 25 and 26, about a core wherein 20 is a mandrel. These conductors are insulated electric wires wound around this mandrel with their ends at an angle to the mandrel and equally spaced apart and of equal extended lengths. This particular operation is most conveniently performed by placing the mandrel in a jig, which jig holds the copper conductors in spaced relationship with each other and the mandrel and allows winding the conductors about the mandrel. This forms a comb.

The second step in this process is to form a plastic body 27 about the comb, which body includes the ends of the wires 22 to 26 shown in Fig. 2. The plastic body holds the wires insulated from each other in their original spaced relationship. The use of the mandrel 20, shown in Figs. 1, 2, 3 and 4 is advantageous to center the assembly but is not necessary as the mandrel may be removed after forming the wire comb. The comb is held in spaced relationship as shown in Fig. 3, the ends of the wire protruding as shown in Fig. 2, for purposes of illustration at substantially right angles to the mandrel and all lying in the same plane. It is not necessary that they be so arranged, as the angle could be other than a right angle and the ends need not lie in the same plane. The only requirement is that they be spaced apart in such a manner that when the ring retaining recesses are cut in the later step of this process, that such recesses contact one and only one of the conductors.

Fig. 3 shows a view of the assembly as cast at right angles in profile to that shown in Figure 2.

The next step in this process is the reduction of the plastic body 27 to the desired size, which is slightly greater than the finished product and at the same time to machine the ring receiving recesses 28, shown in Fig. 4, each of which recesses contact a single conductor and expose the end thereof. This assembly is shown in Fig. 5 at right angles to the wire shown in Fig. 4 wherein the insulator 27 is formed about the mandrel 20 as an axis and has the conductors 21 to 26 each within the ring re ceiving recesses 28, 29, 30, 31, 32 and 33. For purposes of convenience in illustration the electrical conductors are shown in the center of the recesses at the bottom thereof. The recesses could have been so machined that the conductors 21 to 26 could have been partially included and therefore the electrical contact, although it is shown in the center, at the bottom of the recess, could have been along the sides thereof, but under either of these. possibilities the electrical conductor wound around the core leads-through the plastic to the'surface of this recess.

The plastic body, including the ends of the electrical conductors is then coated with a conductive coating. This is shown at 34 in Fig. 7. This coating may be deposited by the chemical reduction method or by the vacuum metallizing method, or by other methods. The article is then introduced into an electrolytic bath, the con ductive coating being used as a terminal and a heavy deposit of a metal is plated on the coating 34. This deposit 35 of Fig. 8 may be silver or silver alloy but it could be copper or any other metal that is desired, silver and its alloys being the preferred metal. This assembly is then machined to a finished size removing the excess metal coating 34 and 35 and leaving the rings 36, 37, 38, 39, 40 and 41 as shown in Fig. 9 separated by the insulators formed from the sides of the ring receiving recesses 28 to 33, shown in Fig. 5. These rings are connected directly to the electrical conductors 21 to 26, shown in Fig. 9, in the partially sectional view. A hard surface plating such as tungsten, cadmium or chromium may be plated on these conductors to give the surface wearing properties necessary to withstand the continuous abrasion of the brushes.

It has been found if silver is used to form the conductive coating 34 shown in Fig. 7 and the usual ammoniacal silver nitrate solution is reduced to precipitate the metal on the plastic there is a tendency for the copper to react with said solution to form copper salts 21a around the surface of the leads. This is shown in Fig. 6, wherein an enlarged view of one of the ring receiving recesses and the copper lead 21 in the bottom thereof is shown. This copper salt 21a forms over the surface of the copper and a small area adjacent thereto and is not a good conductor, and therefore the metal plated thereon does not form a good contact with the lead.

In order to overcome this difficulty it has been found sometimes desirable after machining the ring receiving recesses and before coating the assembly with the conductive coating 34, to electro-plate the surface of the copper leads with silver plating using the leads as one terminal in the plating solution. These copper leads, after they have been silver plated have no tendency to react with the ammoniacal silver solution used to precipitate the conductive coating 34 upon which is plated the massive metal 35.

An alternative method, which comes within the scope of this invention, is to form a core assembly as shown in Fig. 10. This method consists in looping the wires about the core in such a manner that the wire loops are contacted by the ring receiving recesses 42, 43 and 44, shown in Fig. 11, and thereby exposing a part of said loop so that electrical contact is made with these loops at the bottom of the ring receiving recesses, shown in Fig. 11.

The above embodiments of this invention have been given as illustrative only of a method of forming slip ring assemblies located on the surface of an insulator, the surface being parallel to the axis thereof. They can be located on a surface at right angles to this axis, as shown in Fig. 12, wherein the leads 45, 46 and 47 come to the surface 48 of the plastic insulator body formed thereon. These leads are spaced at definite distances from the core and when out as at 13, 13, shown in Fig. 12, an end view of which is shown in Fig. 13, the leads terminate in the surface and may have machined therein conductor retaining slots 14, 15, 16, 17, 18 and 19 (as shown in Fig. 4) to receive and hold electrical conductors similar to the rings referred to above, but located in the end of the insulator body, which conductors may be used for timing devices wherein a series of contacts could be made in one revolution of the shaft 49. This device is made from a comb similar to that referred to in the first embodiment of this invention wherein the strands of the leads are parallel with the axis of the core.

Still another embodiment of this invention comprises the assembly of a comb similar to that shown in Fig. 1

about a central core, which comb is introduced into a mold 50 (shown in Fig. 14) wherein the leads 21 to 26 are in excess length so that when the mold closes the leads are cut by the mold, the plastic is then caused to flow into the mold and the leads 21 to 26 are formed within the ring receiving recesses 28 to 33 shown in Fig. 14, the ring-forming recesses are formed by the part 51 of the mold 50. The plastic may be of any desired type and is not limited to a transparent plastic because the machining steps in the formation of the blank assembly are not necessary. This assembly may be coated with the conductive coating 34, shown in Fig. 7, and the proccess completed. This also allows the production by molding of slip rings wherein the ring receiving recesses are not complete circles.

While several embodiments of this invention are given above, it is apparent to one skilled in the art that many variations and changes may be made therein, all including the invention as set forth in this specification and claimed herein.

What is claimed is:

l. A slip ring assembly comprising a rotatable shaft, a plurality of separate, insulated, conductor wires wrapped around the shaft, insulating material molded around said shaft and wires and holding them in assembled position, said insulating material having circumferentially extending grooves in its outer surface near one end, and conductors in said grooves, said wires having outwardly projecting, spaced apart ends extending through the insulating material to thebottoms of said grooves and being attached respectively to the conductors in said grooves.

2. A slip ring assembly comprising a rotatable shaft, a plurality of separate, insulated, conductor wires wrapped around the shaft, insulating material molded around said shaft and wires and holding them in assembled position, said insulating material having continuous annular grooves in its outer surface near one end, slip rings in said grooves. said wires having outwardly projecting spaced apart ends extending through the insulating material to the bottoms of said grooves and being attached respectively to the slip rings in said grooves.

3. In a process of forming electrical conductors, the steps of forming a comb by assembling insulated wires about a central mandrel with the ends of the wires at right angles to the mandrel and spaced predetermined distances apart, forming a plastic body around the mandrel including said comb, forming circumferential grooves in said plastic body intersecting each wire of said comb, silver electro-plating the end of the wire in each groove, chemically depositing a silver coating on at least the grooved portion of the plastic assembly, silver electroplating at least, that portion of the assembly including the groove, to a height exceeding the depth of said groove, machining the peripheral portion of the assembly to remove any excess silver and plastic and to form the final assembly.

4. In a process of forming electrical conductors, the steps of forming a comb by assembling insulated wires about a. central mandrel with the ends of the wires at right angles. to the mandrel and spaced predetermined distances apart, forming a plastic body around the mandrel including said comb, forming circumferential grooves in said plastic body intersecting each wire, chemically depositing a silver coating on at least the grooved portion of the plastic assembly, silver electro-plating at least that portion of the assembly including the groove to a height exceeding the depth of said groove, machining the peripheral portion of the assembly to remove any excess silver and plastic and to forrnthe final assembly.

5. In a process of forming electrical conductors, the steps of forming a comb by assembling insulated wires about .a central mandrel with the ends of the wires at right angles to the mandrel and spaced predetermined distances apart, molding a plastic body with circumferential grooves around the mandrel including the comb, each of said grooves intersecting a single wire, applying a conductive 5 coating on at least that portion of the assembly including the groove, electro-plating to a height exceeding the depth of said groove, machining the peripheral portion of the assembly to remove any excess metal and plastic and to form the final assembly. 5

References Cited in the file of this patent UNITED STATES PATENTS 1,339,987 Smith May 11, 1920 10 6 Blackburn Mar. 6, 1923 Varner Mar. 27, 1928 Moeller Apr. 13, 1943 Meyerhoefer May 21, 1946 Hanna Dec. 7, 1948 OTHER REFERENCES Worth, T. R: Abstract of application Ser. No. 702,720, published July 12, 1949, O. G. 638. 

